Fluid processing for separating emulsions

ABSTRACT

Fluid processing apparatus comprising a vessel containing a hydrocyclone and defining an inlet chamber, the vessel having a vessel inlet arranged to feed fluid into the inlet chamber, being arranged to receive fluid from the vessel inlet and to pass the fluid to an inlet of the hydrocyclone. The inlet chamber includes coalescing means arranged to coalesce relatively small droplets contained in the fluid received at the vessel inlet into larger droplets before passing the fluid to the hydrocyclone inlet. The coalescing means having a substantially predetermined external shape which defines at least one elongate liner hole for receiving a respective hydrocyclone liner.

This invention relates to fluid processing apparatus comprising a vesselcontaining a hydrocyclone.

EP-A-0734751 discloses a cylonic separator having coalescing mediaplaced around the cyclone liners and through which fluid to be separatedis forced to flow prior to entering the cyclone liners. In oneembodiment the coalescing means is mounted on sleeves which are directlymounted on the cyclone liners. The configuration of the coalescing meansand cyclone liners in this sleeved embodiment removal or insertion ofthe cyclone liners independently of the coalescing means.

According to a first aspect of the invention, there is provided fluidprocessing apparatus comprising, a vessel containing a hydrocyclone anddefining an inlet chamber, the vessel having a vessel inlet arranged tofluid into the inlet chamber, and the inlet chamber being arranged toreceive fluid firm the vessel inlet and to pass the fluid to an inlet ofthe hydrocyclone, the inlet chamber including coalescing means arrangedto coalesce relatively small droplets contained in fluid received at thevessel inlet into larger droplets before passing the fluid to thehydrocyclone inlet, the coalescing means having a substantiallypredetermined external shape which defines at least one elongate linerhole for receiving a respective hydrocyclone liner and which permitsremoval of the hydrocyclone liner without removing the coalescing means.

By arranging for the coalescing mean to have a substantiallypredetermined external shape, it is possible to fit the coalescing meansto existing fluid processing apparatus. Futhermore by defining at leastone elongate liner hole for receiving a respective hydrocyclone liner,the difficulties of the hydrocyclone liner becoming entangled with thecoalescing media or causing disruption of the coalescing media when theliner is removed, are avoided. For example, in the preferred embodimentwhich includes a region of generally parallel fibres which extendgenerally parallel to the direction of fluid flow, without ensuring thatthe coalescing media defines an elongate liner hole, it has been foundthat the parallel fibres restrict entry of the hydrocyclone liners andalso become disrupted when hydrocyclone liners are removed because theytend to stick to or snag on the external surface of the liners.

In one embodiment, the substantially predetermined external shape of thecoalescing means is produced by the coalescing means including a cageassembly dimensioned to allow it to fit inside the hydrocyclone vesselinlet chamber. Grids may be provided at various points along the cage toallow different stages of coalescing media to be supported. Means mayalso be provided to segregate the coalescing media from thehydrocyclones to allow passage of the hydrocyclone through the media forease of installation and removal. The cage assembly may also provide abaffle to divert incoming flow to one end of the hydrocyclone vesselinlet chamber causing a plug flow regime through the media prior tofluid entering the hydrocyclone.

In a second aspect, the invention provides a method of manufacturingfluid processing apparatus having a vessel containing a plurality ofhydrocyclones and defining an inlet chamber, the vessel having a vesselinlet arranged to feed fluid into the inlet chamber, and the inletchamber being arranged to receive fluid from the vessel inlet and topass the fluid to the respective inlets of the hydrocyclones, comprisingthe steps of inserting a mass of coalescing media into the inletchamber, the media having a substantially predetermined external shapedefining at least one elongate liner hole for receiving a respectivehydrocyclone liners and being arranged to coalesce relatively containedin fluid received at the vessel inlet into larger droplets beforepassing the fluid to the respect hydocyclone inlets and subsequentlyinserting at least one hydrocyclone liner into a respective liner hole.

In a third aspect, the invention provides a method of manufacturingfluid processing apparatus having a vessel containing a plurality ofhydrocyclones and defining an inlet chamber, the vessel having a vesselinlet arranged to feed fluid into the inlet chamber, and the inletchamber being arranged to receive fluid from the vessel inlet and topass the fluid to the respective inlets of the hydrocyclones, the inletchamber including coalescing means arranged to coalesce relatively smalldroplets contained in fluid received at the vessel inlet into largerdrop before passing the fluid to the respective hydrocyclone inlets,comprising the step of locating an inlet arrangement in the inletchamber, the inlet arrangement having an inlet baffle which divides theinlet chamber into an inner region which contains the hydroyclones andan outer region adjacent the interior surface of the vessel wall thevessel inlet being arranged to feed fluid into the outer region and theinner region containing a mass of fibrous coalescing medium whose fibresare attached at one end and which at least in use, are arrangedgenerally parallel to the flow direction of fluid in the inner region.

Fluid processing apparatus embodying the invention will now be describedby way of example with reference to the drawings in which:

FIG. 1A is a schematic view of a prior art hydrocyclone;

FIG. 1B shows a closed overflow outlet of a hydrocyclone;

FIG. 1C shows an overflow and underflow outlet of a hydrocyclone coupledtogether;

FIG. 2 is a sectional view through a vessel;

FIG. 3 is an elevational view of an inlet arrangement;

FIG. 4 is a partial section through the inlet arrangement of FIG. 3assembled to the vessel of FIG. 2; and

FIG. 5 is a schematic view of a coalescer structure.

With reference to FIG. 1A, a typical configuration for a hydrocyclonehas a conical section 2, a swirl chamber 4, which is generallycylindrical, and a vortex finder 6, which extends into the swirl chamber4.

In the case of a de-oiling hydrocyclone, oily water is fed tangentiallyat high velocity into an inlet 8 to the swirl chamber 4 which causes avortex flow pattern within the hydrocyclone. The vortex creates a highacceleration field of the order of 1000-3000 g which forces the lighteroil droplets to migrate to the central axis of the hydrocyclone. Due todiffering axial pressure gradients, the heavier material (the water)flows out through an underflow 10 at the tapered end of the conicalsection 2 and the oil core flows in the opposite direction and exits thehydrocyclone via the overflow 12.

On a simple level, the separation performance of a hydrocyclone isrelated to the radial velocity achieved by a drop of a given diametertravelling towards the axial core of the hydrocyclone. Under a givenacceleration field within the hydrocyclone, a modified form of Stoke'slaw describes this radial velocity. The relationship may be defined bythe formula$u_{s} = \frac{G\quad g\quad \Delta \quad {\rho d}^{2}}{18\mu}$

where u_(s) is the radial velocity, Gg is the acceleration field createdby the spinning flow, Δp is the phase density difference between the oiland water, d is the oil droplet diameter and μ is the continuous phase(water) viscosity. Since an increase in the velocity u_(s) produces acorresponding increase in the likelihood that the drop will reach theoil core (and therefore be separated) before being carried out with thewater in the underflow, it is desirable to increase that velocity.

Having noted that the drop diameter is a squared term in the formula, itis noted that only a small increase in droplet size will provide a largeincrease in separation performance. It has been found for example thatfor a typical high efficiency de-oiling hydrocyclone, an increase indrop size entering the inlet 8 from 5 μm to 10 μm increases theseparation efficiency from 15% to over 90%.

With reference to FIG. 2, a plurality of hydrocyclones 18 are fittedwithin a vessel 20. The vessel has an inlet 22 for oily water, an oiloutlet 24 and a water outlet 26.

The hydrocyclones 18 are fixed in a generally parallel configurationbetween two hydrocyclone support plates 26,28. The hydrocyclone supportplates 26,28 are generally planar with holes to receive hydrocycloneliners of the general configuration shown in FIG. 1. The left-handsupport plate 26 receives the overflow 12 and the right-hand supportplate 28 receives the underflow 10. The overflow and underflowrespectively are sealed to the support plates 26,28 and thus the vessel20 is divided into three chambers; an oil outlet chamber to the left ofthe support plate 26, a water outlet chamber to the right of the supportplate 28 and an inlet chamber between the plates 26 and 28. Other vesselconfigurations are used. For other configurations, the general principleof passing the fluid through a coalescing medium in the inlet chambershould be followed.

The inlet 22 feeds oily water into the inlet chamber which exits theinlet chamber via the plurality of hydrocyclone inlets 8. These arelocated generally in the region marked 23 in FIG. 2.

The hydrocyclone liners are surrounded by a fibre-based coalescingstructure 30. The coalescing structure is described in more detail belowbut, put briefly, this has the function of enlarging the droplet size toimprove separation performance as described above.

An inlet device 32 having a so-called “top hat” configuration is shownseparately in FIG. 3. The inlet device has a baffle 34 of smallerdiameter than the internal diameter of the vessel 20. The inlet deviceis arranged to be located within the inlet chamber just to the left ofthe hydrocyclone support plate 28. The inlet device 32 is sealed againstthe hydrocyclone support plate 28 by a sealing ring 36. It is fixed tothe support plate 28 by bolts passing through the support plate and theinlet device. At the left end of the inlet device 32 (as shown in theFigure) an enlarged diameter portion is formed which has a diameter justless than the internal diameter of the vessel 20. Thus, a second scalingring 38 may be used to seal the inlet device 32 against the internalsurface of the vessel 20.

The inlet device 32 is inserted within the inlet chamber generally inthe region 39 as shown in FIG. 2.

With reference to FIG. 4, the flow of oily water through the inletdevice 32 is shown generally by arrows 40. It will be seen that thebaffle 34 defines a generally concentric outer region with the generallycylindrical wall of the vessel 20. Apertures 42 are formed in the baffle34 at the right side of the inlet device 32 adjacent the cyclone supportplate 28. Thus, fluid flowing into the inlet 22 is guided along theouter region generally to the right in FIG. 4 and then through theapertures 42. The apertures 42 generate a radially inward flow into theright side of the fibre-based coalescing structure 30. This arrangementcreates a so-called “plug flow” flow regime.

It will be appreciated that before the fluid which has passed throughthe apertures 42, can enter the cyclones 18, it must travel practicallythe full length of the inlet chamber. In doing so, it is caused to passthrough the coalescing structure 30. This coalescing structure isarranged to increase the droplet size of the oil in the oily waterthereby to improve separation efficiency of the hydrocyclones 18.

The choice of the fibre-based coalescing structure is a compromisebetween high flow rate and good coalescing performance. To achieve goodperformance, the coalescing structure should consist of fine, highdensity media where contact time with the media is maximized by limitingflow velocity through the media. However, this type of media issusceptible to solids fouling and would therefore require periodicmaintenance by replacement. This type of coalescing structure is usedwith gravity separators where large droplet sizes are very important.However, as described above, since in the case of a cyclonic separator,the droplet size has an exponential relationship with separationperformance, it has been realized that some coalescing performance maybe sacrificed (in order to improve throughput) with little impact on theoverall hydrocyclone performance. Thus, the present invention uses acoalescing media of relatively low density which is generally notaffected by solids fouling problems. Furthermore, the inlet device 32 isarranged to minimize “short circuit” flows and to ensure that fluidflows through most if not all of the coalescing structure 30, therebymaximizing the flow residence time through the coalescing fibre media.

The fibres in the coalescing structure 30 are preferably relativelysmall. This enhances the entrapment efficiency of the fibres which inturn allows a lower residence time in the inlet chamber to achievesufficient droplet size and this in turn, allows a greater flow velocitythrough the coalescing material and therefore through the vessel as awhole.

However, prior art designs have used fibres which extend radially from acentral point. Fibres of sufficiently small diameter to provide goodentrapment have insufficient strength to withstand the drag forceimparted by the fluid flow in the prior art arrangement and also becomeclogged where the fibres are close together.

Additionally, the fibre density (i.e. the ratio of the volume of fibresper unit volume) has been found to be an important factor in coalescenceperformance.

Thus the coalescing structure 30 preferably has a fibre constructionwhich incorporates one or more different coalescing media which may havediffering fibre density, fibre diameter and fibre surface chemistrywetting properties which vary across the axial length of theprecoalescer formed by the coalescing structure 30 in the inlet chamber.The fibres of the coalescing structure 30 may be surface treated to varythe wettability of the fibres. This may be used to adjust the coalescingperformance.

As an example, a suitable construction for the coalescing structure 30has three stages of coalescing media.

Ideally, for efficient droplet capture, the fibre diameter should be ofa similar diameter to the diameter of the droplets of interest.Preferably also, the fibres are hydrophobic.

Since the efficiency of a hydrocyclone tends to fall away as the inletdrop size distribution falls below a particular threshold which dependson the hydrocyclone geometry, the physical properties of the phasesinvolved and the operating conditions, the first stage fibre diameter isselected to be approximately equal to that drop size distribution.However, as described above, fibres of this diameter are notstructurally robust and thus it has proved difficult to develop a mediumwhich has small diameter fibres but also has a sufficiently highporosity to ensure that it is not susceptible to solids fouling. Thisproblem has been overcome by using a “tow” which is constructed fromfine fibres having a similar diameter to the dispersion droplets andwhich are grouped in the same direction as the fluid flow. This mediumis typically attached at one end only near the support plate 28. Asfluid flows through the apertures 42 and back towards the hydrocycloneinlets 8, the fibres align themselves generally parallel with the flowdirection. This arrangement exhibits a low pressure drop andinsensitivity to solids fouling but a high droplet capture efficiency.Furthermore, the fibres are strong in tension and therefore have a longservice life. Typical materials for the fibres are stainless steel,glass fibre, polypropylene or polyester. A typical diameter would be inthe range of 5 μm to 20 μm.

Preferably, the fibres are attached to a grid which is fixed to theinlet device in its inner region generally adjacent the apertures 42.Thus the inlet device and the first stage of the coalescing structuremay be inserted into the vessel 20 as a complete pre-assembled unit. Inthis case, the first stage of the coalescing structure 30 would form theportion marked 46 in FIG. 2.

The tow may be attached at both ends. The attachment points in thiscase, would be arranged to cause the fibres to be aligned generally withthe direction of flow through the coalescing medium at that point. Itmay instead be advantageous to align the fibres at a small angle ofinclination to the direction of flow. Provided the angle of inclinationis not too great, the fibres will be sufficiently strong to withstandthe drag forces imparted by the fluid as it passes through thecoalescing medium.

As the fluid flows towards the hydrocyclone inlet 8, it passes through asecond stage formed from a coarse mesh having a larger fibre diameterthan the tow. The larger fibre diameter (typically 20 μm to 30 μm)allows the fibre diameter/droplet diameter ratio to be near unity whichin turn enhances the coalescing efficiency. The medium may be made froma similar choice of materials to that of the tow.

The third stage, which is located downstream of the second and firststages, may be formed from an open mesh (having a fibre diameter largerthan that of the second stage; typically 400 μm). The open mesh may, forexample, be made from polyester, nylon or PTFE.

Preferably, the coalescing structure 30 is formed with pre-formed holesfor the insertion of one or more hydrocyclone liners. Thus, a vessel 20may be assembled by opening the vessel by the removal of the supportplate 26, inserting an inlet device 32 (with or without the fine fibrefirst stage coalescing structure described above already attached), anintegrally-formed coalescing structure 30 (which may include the secondand third stages described above) may be inserted into the vessel andthen the individual hydrocyclone liners may be inserted into the holesin the coalescing structure 30. Finally, the hydrocyclone support plate26 is fixed to close the vessel. Since these components are modular,they may be readily maintained and furthermore may be fittedretrospectively to existing vessels. It will be appreciated that onecoalescing stage may be used or more than one, and the number of stagesis not limited to three as described above.

With reference to FIG. 5, the coalescing structure 30 is shown separatedfrom the vessel and hydrocyclone liners.

A support frame 50 is used to mount the coalescing structure within avessel. The means has a media cage 54 which is formed of a plurality ofmedia support grids 52 to which are fixed “parallel” coalescing media56.

The coalescing means may also include floating tubes 58 which allow easyinsertion and removal of hydrocyclone liners.

The vessel may be used to separate oil from water or water from oil orby correct selection of the coalescing media and the hydrocyclonedimensions, other fluids.

It will be understood that a “hydrocyclone liner” means an individualhydrocyclone with the necessary interfaces to allow it to be installedinside a pressure vessel.

What is claim is:
 1. Fluid processing apparatus comprising: a vesselcontaining a hydrocyclone and defining an inlet chamber, the vesselhaving a vessel inlet arranged to feed fluid into the inlet chamber, andthe inlet chamber being arranged to receive fluid from the vessel inletand to pass the fluid to an inlet of the hydrocyclone, the inlet chamberincluding coalescing means mechanically supported by the vessel andarranged to coalesce relatively small droplets contained in fluidreceived at the vessel inlet into larger droplets before passing thefluid to the hydrocyclone inlet, the coalescing means having asubstantially predetermined external shape which defines at least oneelongate liner hole for receiving a respective hydrocyclone liner andwhich permits removal of the hydrocyclone liner without removing thecoalescing means.
 2. Apparatus according to claim 1, wherein thecoalescing means is arranged to cause the fluid to pass through fibersof generally increasing. respective cross-sectional areas as the fluidpasses towards the hydrocyclone inlet.
 3. Apparatus according to claim1, wherein the coalescing means is arranged to cause the fluid to passthrough fibers of predetermined varying wettability as the fluid passestowards the hydrocyclone inlet.
 4. Apparatus according to claim 1,wherein the coalescing means is arranged to cause the fluid to passthrough fibers and wherein the coalescing means is further arranged tocause the fluid to pass through regions in which the fiber densityvaries in a predetermined manner as the fluid passes towards thehydrocyclone inlet.
 5. Apparatus according to claim 1, wherein thecoalescing means includes a region of generally parallel fibersarranged, at least in use, to extend generally parallel to the directionof fluid flow.
 6. Apparatus according to claim 5, wherein the parallelfibers are attached generally by one end only of the fibers. 7.Apparatus according to claim 5, wherein the fibers are attached at bothends.
 8. Apparatus according to claim 1, wherein the inlet chamberincludes an inlet arrangement which creates a plug flow regime at theinlet of the coalescing means.
 9. Apparatus according to claim 1,wherein the vessel is generally elongate and the hydrocyclone inlet ispositioned generally at a first end of the vessel, the inlet chambercontaining an inlet arrangement having an inlet baffle which divides theinlet chamber into an inner region which contains the hydrocyclone andan outer region adjacent a interior surface of the vessel wall, thevessel inlet being arranged to feed fluid into the outer region and theinlet baffle including at least one baffle aperture located generally ata second, distal end of the vessel and arranged to permit fluid flowfrom the outer region to the inner region.
 10. Apparatus according toclaim 9, wherein the inner region further contains the coalescing means.11. Apparatus according to claim 9, wherein the vessel inlet is arrangedto feed fluid into the outer region at a position between the two endsof the vessel.
 12. Apparatus according to claim 9, wherein the outerregion extends along a shorter length of the vessel than the innerregion.
 13. Apparatus according to claim 9, wherein the inlet baffle isgenerally cylindrical.
 14. Apparatus according to claim 13, wherein eachbaffle aperture is arranged to cause a generally inwardly radial flow offluid into the inner region.
 15. Apparatus according to claim 9, whereinthe parallel fibers extend in the inner region from each baffle aperturetowards the first end of the vessel.
 16. Apparatus according to claim 1,wherein the coalescing means includes a mass of integrally-formedcoalescing media defining a plurality of elongate holes for receiving atleast one respective hydrocyclone liner.
 17. Apparatus according toclaim 1, wherein the fluid is an oil and water emulsion.
 18. Apparatusaccording to claim 1, wherein the overflow outlet of the hydrocyclone isclosed.
 19. Apparatus according to claim 1, wherein the overflow andunderflow outlets of the hydrocyclone are coupled together. 20.Apparatus according to claim 1, wherein the vessel contains a pluralityof hydrocyclones.
 21. A method of manufacturing a fluid processingapparatus having a vessel containing a plurality of hydrocyclones anddefining an inlet chamber, the vessel having a vessel inlet arranged tofeed fluid into the inlet chamber, and the inlet chamber being arrangedto receive fluid from the vessel inlet and to pass the fluid to therespective inlets of the hydrocyclones, comprising the steps of:inserting a mass of coalescing media into the inlet chamber, the mediahaving a substantially pre-determined external shape defining at leastone elongate liner hole for receiving each respective hydrocycloneliner, and arranging said coalescing media to coalesce relatively smalldroplets contained in fluid received at the vessel inlet into largerdroplets before passing the fluid to each respective hydrocyclone inlet,subsequently inserting at least one hydrocyclone liner into a respectiveliner hole and mechanically supporting said coalescing media on saidvessel.
 22. A method according to claim 21, including the step oflocating an inlet arrangement in the inlet chamber, the inletarrangement having an inlet baffle which divides the inlet chamber intoan inner region which contains the hydrocyclones and an outer regionadjacent an interior surface of a vessel wall, arranging the vesselinlet to feed fluid into the outer region and the inner regioncontaining a mass of fibrous coalescing medium whose fibers are attachedat one end of the vessel and arranging said fibers so that they are, atleast in use, generally parallel to the flow direction of fluid in theinner region.
 23. A method of manufacturing a fluid processing apparatushaving a vessel containing a plurality of hydrocyclones and defining aninlet chamber, the vessel having a vessel inlet arranged to feed fluidinto the inlet chamber, and the inlet chamber being arranged to receivefluid from the vessel inlet and to pass the fluid to respective inletsof the hydrocyclones, the inlet chamber including coalescing meansarranged to coalesce relatively small droplets contained in fluidreceived at the vessel inlet into larger droplets before passing thefluid to the respective hydrocyclone inlets, comprising the steps of:locating an inlet arrangement in the inlet chamber, the inletarrangement having an inlet baffle which divides the inlet chamber intoan inner region which contains the hydrocyclones and an outer regionadjacent the interior surface of the vessel wall, arranging the vesselinlet to feed fluid into the outer region and the inner region, whereinthe coalescing means in said inner region contains a mass of fibrouscoalescing medium whose fibers are attached at one end of the vessel andarranging said fibers so that they are, at least in use, generallyparallel to the flow direction of fluid in the inner region.
 24. Amethod of manufacturing according to claim 23, additionally includingthe step of mechanically supporting said coalescing means by saidvessel.